Narrative:

Madison to eau claire. I filed for and was cleared for 4000 ft en route. The flight was conducted in IFR conditions from the dells north. After entering clouds I added carburetor heat and pitot heat and proceeded normally. The outside temperature was 0 fahrenheit. There was no indication of ice on wings or windscreen. Approximately at tomah the engine coughed and almost died. I notified chicago center of the problem and indicated that I did not wish to declare an emergency. I switched tanks, mags, and changed carburetor heat to no avail. Reducing the throttle brought the engine back to running smoothly at 15 inches. That power setting was insufficient to maintain altitude without stalling. Altitude dripped to 3000 ft before I was able to add sufficient power to initiate a slow climb back to 4000 ft. I considered landing at black river falls but changed my mind. The engine began to run normally and the approach at black river would be an ADF to near mins. I lost radio contact with chicago center and was unable to establish contact with minneapolis center. Eventually contact with minneapolis center was reestablished. I received a clearance for an ILS approach to 22 at eau claire. Perhaps in the anxiety of the situation, I failed to verify the OM and proceeded well past the approach course. When I realized the mistake I declared a missed approach and proceeded to the VOR inbound. Conditions at eau claire had improved so that at 3000 ft. I had ground contact throughout the approach. While proceeding toward the VOR I realized I was over the field. I advised center that I would cancel IFR and land since I was in VFR conditions and had the field in sight. 2 mechanics have looked at the engine. There are 2 theories: 1. When I chose carburetor heat for an extended operation without leaning the mixture, that may have fouled the plugs. The fouled plugs would operate at reduced power giving the opportunity to go on to eau claire. 2. The aircraft I fly is an small aircraft that has no alternate air. The air cleaner element is foam rubber and on landing in eau claire was found to be saturated with water. It is possible that the moisture froze during the flight and that the reduced air available to the engine contributed to a rich operation that could have fouled the plugs. The plugs are in reasonable shape and have operated normally since this incident. Callback conversation with reporter revealed the following information. Maintenance is convinced the problem was caused by fouled plugs as a result of not leaning and the continuous use of carburetor heat. They do not feel the air cleaner element had anything to do with the loss of power. The plugs have been changed and the aircraft operates fine. It is owned by a club and no other members have had any problems.

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Original NASA ASRS Text

Title: LOSS OF PWR IN IMC CONDITIONS DEV FROM ALT.

Narrative: MADISON TO EAU CLAIRE. I FILED FOR AND WAS CLRED FOR 4000 FT ENRTE. THE FLT WAS CONDUCTED IN IFR CONDITIONS FROM THE DELLS N. AFTER ENTERING CLOUDS I ADDED CARB HEAT AND PITOT HEAT AND PROCEEDED NORMALLY. THE OUTSIDE TEMP WAS 0 FAHRENHEIT. THERE WAS NO INDICATION OF ICE ON WINGS OR WINDSCREEN. APPROX AT TOMAH THE ENG COUGHED AND ALMOST DIED. I NOTIFIED CHICAGO CENTER OF THE PROBLEM AND INDICATED THAT I DID NOT WISH TO DECLARE AN EMER. I SWITCHED TANKS, MAGS, AND CHANGED CARB HEAT TO NO AVAIL. REDUCING THE THROTTLE BROUGHT THE ENG BACK TO RUNNING SMOOTHLY AT 15 INCHES. THAT PWR SETTING WAS INSUFFICIENT TO MAINTAIN ALT WITHOUT STALLING. ALT DRIPPED TO 3000 FT BEFORE I WAS ABLE TO ADD SUFFICIENT PWR TO INITIATE A SLOW CLB BACK TO 4000 FT. I CONSIDERED LNDG AT BLACK RIVER FALLS BUT CHANGED MY MIND. THE ENG BEGAN TO RUN NORMALLY AND THE APCH AT BLACK RIVER WOULD BE AN ADF TO NEAR MINS. I LOST RADIO CONTACT WITH CHICAGO CENTER AND WAS UNABLE TO ESTABLISH CONTACT WITH MINNEAPOLIS CENTER. EVENTUALLY CONTACT WITH MINNEAPOLIS CENTER WAS REESTABLISHED. I RECEIVED A CLRNC FOR AN ILS APCH TO 22 AT EAU CLAIRE. PERHAPS IN THE ANXIETY OF THE SITUATION, I FAILED TO VERIFY THE OM AND PROCEEDED WELL PAST THE APCH COURSE. WHEN I REALIZED THE MISTAKE I DECLARED A MISSED APCH AND PROCEEDED TO THE VOR INBOUND. CONDITIONS AT EAU CLAIRE HAD IMPROVED SO THAT AT 3000 FT. I HAD GND CONTACT THROUGHOUT THE APCH. WHILE PROCEEDING TOWARD THE VOR I REALIZED I WAS OVER THE FIELD. I ADVISED CENTER THAT I WOULD CANCEL IFR AND LAND SINCE I WAS IN VFR CONDITIONS AND HAD THE FIELD IN SIGHT. 2 MECHS HAVE LOOKED AT THE ENG. THERE ARE 2 THEORIES: 1. WHEN I CHOSE CARB HEAT FOR AN EXTENDED OP WITHOUT LEANING THE MIXTURE, THAT MAY HAVE FOULED THE PLUGS. THE FOULED PLUGS WOULD OPERATE AT REDUCED PWR GIVING THE OPPORTUNITY TO GO ON TO EAU CLAIRE. 2. THE ACFT I FLY IS AN SMA THAT HAS NO ALTERNATE AIR. THE AIR CLEANER ELEMENT IS FOAM RUBBER AND ON LNDG IN EAU CLAIRE WAS FOUND TO BE SATURATED WITH WATER. IT IS POSSIBLE THAT THE MOISTURE FROZE DURING THE FLT AND THAT THE REDUCED AIR AVAILABLE TO THE ENG CONTRIBUTED TO A RICH OP THAT COULD HAVE FOULED THE PLUGS. THE PLUGS ARE IN REASONABLE SHAPE AND HAVE OPERATED NORMALLY SINCE THIS INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. MAINT IS CONVINCED THE PROBLEM WAS CAUSED BY FOULED PLUGS AS A RESULT OF NOT LEANING AND THE CONTINUOUS USE OF CARB HEAT. THEY DO NOT FEEL THE AIR CLEANER ELEMENT HAD ANYTHING TO DO WITH THE LOSS OF PWR. THE PLUGS HAVE BEEN CHANGED AND THE ACFT OPERATES FINE. IT IS OWNED BY A CLUB AND NO OTHER MEMBERS HAVE HAD ANY PROBLEMS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.